Many public switched telecommunication networks, PSTN, are in use. Recent switched telecommunication networks are based on digital technology and are designed to be able to transmit various kinds of information at various speeds, e.g speech or data or video.
Public switched telecommunication networks, PSTN, generally comprise network subscriber stores for various information on subscribers to the network e.g identification, type, subscribed services, location or routing etc.
Public switched telecommunication networks generally also comprise means for connecting subscriber equipment to the network, and means for setting up calls to and from connected subscriber equipment in accordance with information in the network subscriber store. Such means may comprise exchanges interconnected by trunks.
When a public switched telecommunication network, PSTN, comprises plural distant local or transit exchanges there may be network subscriber stores at all local exchanges having allocated subscribers.
Some subscribers to a telecommunication network may be residential subscribers having a residential equipment connected by cables to a local exchange of the network.
Some residential subscriber equipments comprise a residential base radio station connected to the network by cable and a cordless telephone or portable radio terminal. The residential base radio station then comprises a residential radio transceiver for radio communication with the portable radio terminal or cordless telephone constituting part of the same subscriber residential equipment. This kind of residential subscriber equipment offers a user the freedom of making calls and receiving calls anywhere in his residence if within reach of his residential radio transceiver.
Other subscribers to a switched telecommunication network may be business subscribers. The subscriber equipment may then be a private automatic branch exchange, PABX, connected by cable to the telecommunication network and plural terminals or telephones constituting extensions to the private branch exchange.
Recently private automatic branch exchanges, PABX, comprising means for communication by radio with associated branch extensions have been suggested. The private automatic branch exchange, PABX, may then comprise an exchange switch connected by cable to a telecommunication network, exchange radio transceivers connected by cable to the exchange switch and portable radio terminals or cordless telephones for radio communication with the exchange radio transceivers. This kind of subscriber equipment may offer a staff the freedom of making calls and receiving calls anywhere in a business area of the subscriber if within reach of any of the exchange radio transceivers.
Many mobile radio communication systems of various kinds have o been suggested and are in use for various purposes. Cellular mobile radio communication systems may cover a very large geographical area offering a user with a mobile station a possibility to make calls at office, in residential areas and in some vehicles. A disadvantage of some mobile communication systems is the high cost, weight and size of mobile stations, the operators high charge for becoming a subscriber and the high charge for a call compared to corresponding costs for a subscriber using a terminal connected by cable to a fixed telecommunication network.
Telepoints have been suggested as a compromise between the low costs and low freedom of fixed telecommunication equipment and the high costs and freedom of cellular mobile radio communication systems. The telepoint concept offers users the possibility of small light-weight battery-powered- portable radio terminals for making calls anywhere via any fixed telepoint radio transceiver. The telepoint radio transceivers may be located at various places such as railway or underground stations, airports, pedestrian areas, squares, in official buildings etc. They are connected by cable to a switched telecommunication network. The telepoint concept requires comparatively little power consumption at the portable radio terminals whereby frequent change of battery is obviated. Information on UK telepoint standard may be found in "MPT 1375, COMMON AIR INTERFACE SPECIFICATION", DEPARTMENT OF TRADE AND INDUSTRY, LONDON 1989.
One major disadvantage of suggested telepoint systems is that a subscriber in proximity of a telepoint transceiver can not be called by an other subscriber to the telecommunication network to which the telepoint transceiver is connected. Thus a user of a radio terminal for telepoints can make calls but not receive calls.